[Zope] XHTML and Zope

Hi! I've got a XHTML-Document with MathML. This document is static and should only be served by zope. The problem is, that in older versions than 2.6.0 it is working, but since this version the document my browser (mozilla) starts loading the document, shows the title and the stops without error. This is strange, because the document is valid and it works with an older version of zope. Is this a bug or did I do something wrong? Thanks Sebastian